Been lurking for a bit... Got into RC in the mid '80s with cars, and then airplanes.

Most of the air time was on a glider, then a little with a Midwest Aerostar .40.

Got back into it a few years ago with cars again, and helis, which I always wanted to do when young but they were a little out of reach for a kid...

I've already found a lot of useful info on this site so just saying Hi!.

My most recent completed project is a Spirit 100 glider by Great Planes. I bought the kit in '92.... A lot of things happened since then, but the short story is I just finished it this spring. It now sports a Park 450 motor, and landing gear, and has had just a few short, mostly straight flights to get it trimmed. Can't wait to get into some thermals!

Been lurking for a bit... Got into RC in the mid '80s with cars, and then airplanes.

Most of the air time was on a glider, then a little with a Midwest Aerostar .40.

Got back into it a few years ago with cars again, and helis, which I always wanted to do when young but they were a little out of reach for a kid...

I've already found a lot of useful info on this site so just saying Hi!.

My most recent completed project is a Spirit 100 glider by Great Planes. I bought the kit in '92.... A lot of things happened since then, but the short story is I just finished it this spring. It now sports a Park 450 motor, and landing gear, and has had just a few short, mostly straight flights to get it trimmed. Can't wait to get into some thermals!

So again, Hello.

Brian

Hey, welcome to the electric model airplane world. The performance of electric power since 92 has exploded in the past 22 years. Now, it's common to hear of someones electric motor pulling 50 Amps, or perhaps a lot more out of some high powered batteries. And, think nothing of it.

In our club, perhaps 90% of models with wingspans under about 50 inches are electric powered.

On my Spirit, I was worried the park 450 would be marginal for power. But it fit within the original cross section of the nose, so I took a gamble. Just the few takeoffs/ landings I have done show that it is plenty of power. Need to try a few different prop sizes but so far so good.

On my Spirit, I was worried the park 450 would be marginal for power. But it fit within the original cross section of the nose, so I took a gamble. Just the few takeoffs/ landings I have done show that it is plenty of power. Need to try a few different prop sizes but so far so good.

On my Spirit, I was worried the park 450 would be marginal for power. But it fit within the original cross section of the nose, so I took a gamble. Just the few takeoffs/ landings I have done show that it is plenty of power. Need to try a few different prop sizes but so far so good.

Brian

Just a note here.
Putting different sized props on a glow or gasoline engine can either result in the engine running to fast, or running two slow, overheating the engine.

Putting to small of a prop on an electric models motor might result in not enough power to get the model off the ground. On the other hand, putting to large of a prop on an electric motor can result in a LOT of power. Until the magic smoke is released from the motor/esc/battery pack.

It is wise to pick up one of those wattmeters to measure the current/voltage/watts being pulled by your motor during wide open throttle. Those wattmeters are fairly inexpensive, and will pay for it self the first time you do NOT burn up something.

Wishing APC had a better range of folding props... I've tried 10x6, 11x8, and 13x7 because that is what they offer. Seems like odd steps in size

Using just my calibrated hand as a guide, the two larger sizes heat the motor up pretty quick. A 30-45 second burst on a 3S is about as far as I want to push it. I've run the 10x6 through a full 2000 maH with very little heat buildup.

These checks were all done on the bench, and maybe in flight the cooling would improve, but I'd like to find a lower pitch 11-12" to try. I'd rather improve the climb performance over gaining speed.

I believe the park 450 requires a 10x5 to a 12x6 prop.
The 12" prop only on 2s. On a 3s I would not go over 9x6 as that motor is only rated for 14amps.
If you go with slow fly props you'll have to size em down another inch.

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This is a fact, you have never been in an empty room.

Been busy with other things..... but finally took the Spirit out tonight for a couple hand launched test glides. Took the landing gear off since the test area was tall rough grass.

Still need to test the motor current but now have a 9x5 prop on it. Should be able to test that as well as get an actual full flight this wknd. Thrust seems marginal for takeoff from ground but should be no problem hand launching.

Motocalc actually predicts this pretty well. Punch in a power system giving a relatively high pitch and high RPM and look at the analysis. It will even say you stalled the prop.

If you turn the prop above the speed here it stalls (turns so fast that the effective angle of attack stalls the blade just like stalling a wing) in static tests it will load up as the aircraft gains speed (un-stalling the prop), then start unloading again as the airspeed gets closer to the speed the prop WANTS to pull the airplane.

There is no definite % of unloading that works every time. It varies a lot with prop and aircraft. For the Spirit, since its a relatively slow model yo want to avoid a prop that you can stall.